googlefonts/roboto-delta

Set axis hidden flag on all Parametric Axes

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#172 opened on Feb 27, 2026

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buggood first issue

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Description

Currently all parametric axes are 'public', so @behdad 's new avar2 partial-instancer ignores them; so please add the flags. Built TTF's TTX should change from e.g. user/public axis then parametric/flagged axis:

    <!-- Grade -->
    <Axis>
      <AxisTag>GRAD</AxisTag>
      <Flags>0x0000</Flags>
      <MinValue>-250.0</MinValue>
      <DefaultValue>0.0</DefaultValue>
      <MaxValue>150.0</MaxValue>
      <AxisNameID>260</AxisNameID>
    </Axis>

    <!-- Parametric Spacing -->
    <Axis>
      <AxisTag>XTSP</AxisTag>
      <Flags>0x0000</Flags>
      <MinValue>-100.0</MinValue>
      <DefaultValue>0.0</DefaultValue>
      <MaxValue>100.0</MaxValue>
      <AxisNameID>261</AxisNameID>
    </Axis>

to

    <!-- Grade -->
    <Axis>
      <AxisTag>GRAD</AxisTag>
      <Flags>0x0000</Flags>
      <MinValue>-250.0</MinValue>
      <DefaultValue>0.0</DefaultValue>
      <MaxValue>150.0</MaxValue>
      <AxisNameID>260</AxisNameID>
    </Axis>

    <!-- Parametric Spacing -->
    <Axis>
      <AxisTag>XTSP</AxisTag>
      <Flags>0x0001</Flags>
      <MinValue>-100.0</MinValue>
      <DefaultValue>0.0</DefaultValue>
      <MaxValue>100.0</MaxValue>
      <AxisNameID>261</AxisNameID>
    </Axis>

Contributor guide

Research direction
Find the code that defines parametric axes in the repository (likely in a Python script using fonttools) and add the flag 0x0001 to the Axis flags for parametric axes to mark them as hidden. Refer to the TTX XML output change in the issue description.
Tech stack
python
Domain
devtools
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Pythonfonttools
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60